The present invention relates to a chemical solubilizing agent for tin or tin alloy used for electroconductive materials such as, for example, printed circuit boards being manufactured, electronic and electric devices.
With electric and mechanical development, the components for use in various devices are being complicated and diversified. For example, in some case in a printed circuit board manufacturing process, tin or tin alloy is plated onto a copper foil layer, etching is applied to unnecessary copper portions, then in a later stage the plated portion alone is removed, and the operation shifts to the next step to form a high precision circuit. Further, there are lead frames and copper wires plated with tin or tin alloy or to which tin or tin alloy is bonded mechanically, and it is sometimes required to remove such coating to expose the copper base as in the case of a printed circuit board. For recovering useful metals such as copper from coating scraps in such manufacturing process or from parts which have become unnecessary, the tin or tin alloy is first removed and then copper is recovered through a copper refining process.
As a method for removing tin or tin alloy from the copper surface containing a copper alloy there has been proposed a method which employs a solubilizing agent (i.e. solvent) containing an oxidizing agent and an inorganic or organic acid as main components. As an improvement over such method there is proposed in Japanese Patent Publication Nos. 40291/1977 and 40292/1977 a method which employs hydrogen peroxide or inorganic peracid ion and acid and fluoride or iron ion as a chemical solubilizing agent for tin-containing metals. Further, as a tin or tin alloy releasing solution there is proposed in Japanese Patent Laid-Open No. 164984/1982 the use of an inorganic or organic acid, an oxidizing agent and a heterocyclic compound of .dbd.NH or .tbd.N not containing a sulfur atom. Further proposed are the combination of iron ion, a hydroxycarboxylic acid and the above heterocyclic compound in Japanese Patent Laid-Open No. 58280/1983; the combination of a fluorine-containing complex ion and the above heterocyclic compound in Japanese Patent Laid-Open No. 74281/1984: the use of polyhydric alcohols in Japanese Patent Laid-Open No. 149790/1985; the combination of a fluorine-containing complex iron, silicate iron and the above heterocyclic compound in Japanese Patent Laid-Open No. 20470/1985; and the use of inorganic and organic acids, peroxides, and organic acids which form a complex with tin ion. In the case of such solubilizing agent using an oxidizing agent for tin or tin alloy, even a simple combination of an oxidizing agent and an inorganic or organic acid dissolves tin or tin alloy relatively easily in the initial stage, but with the lapse of time, tin and other metal ions accumulate in the solubilizing agent solution, making the oxidizing agent unstable, or metallic salts, particularly metastannic acid resulting from the oxidation of tin, precipitates in the solution, so that the solubilizing ability of the solution is deteriorated gradually. To prevent this, as in the prior art referred to above, there has been proposed the use of fluoride ion, a fluorine-containing complex, and an organic acid which forms a complex with tin ion. Further, in some electroconductive materials it is required that only a tin or tin alloy coating on the surface of a copper plate or copper wire be dissolved and the copper surface be made difficult to dissolve. To this end it has been proposed to use heterocyclic compounds of .dbd.NH or .tbd.N, e.g. pyrazole, imidazole, triazole derivatives. It has also been proposed to use polyhydric alcohols in order to enhance the luster of the copper surface.
In those solubilizing solutions, however, the dissolution speed of tin or tin alloy is low, that is, the working efficiency is poor; besides, there often remains tin on the copper surface. Moreover, with deterioration of the solubilizing solution and the resulting increase of the tin concentration in the bath, hydrogen peroxide becomes unstable, resulting in that the effect of the solubilizing solution is deteriorated.
It is the object of the present invention to eliminate the above-mentioned drawbacks of the prior art, particularly provide a solubilizing agent capable of dissolving and removing tin or tin alloy from a copper surface rapidly and capable of stabilizing hydrogen peroxide contained therein, as well as a method therefor.